My downpipe (from pre-cat to cat pipe) flange on the cat side) broke off, and so I'm replacing it. I was able to get the old one off, but one of the studs in the pre-cat broke. It appears to be an M10x1.25 stud, but I have no idea how to get it out. I tried putting a nut on and welding it, but I can't get ANY penetration into the stud, probably because it's overhead and the weld pool wants to run away from the stud. As soon as I try to turn it with any torque the nuts just breaks free. Anyone have any suggestions as to how to get it off, and what is the appropriate replacement size? I've hard 35 mm is probably about right. If I can't get it off, how bad will the leak be with just two nuts, and is there anything I can do to seal it better?